Socket Select problem

Hi

I'm having a little trouble with the select and fork for the server side program that I'm building. The problem is I got the socket and everything working and the basic problem can receive and display the data out. But whenever I put in the select with the fork, the program does not receive and display the data anymore. Can someone point me into the right direction of the problem that I have with the code?

sd is the listening socket descriptor and sd2 is the accepted socket descriptor.

Code:

while (1) {

   		
		result = select(sd, &fds, NULL, NULL, NULL);
		printf("%d", result);
		if (result > 0) 
		{
			printf("entered");
	 		if (FD_ISSET(sd, &fds)) 
			{

				alen = sizeof(cad);
				if ( (sd2=accept(sd, (struct sockaddr *)&cad, &alen)) < 0) {
					fprintf(stderr, "accept failed\n");
					exit(1);
				}

				//make child process
				printf("forking now");
				pid = fork();

				if (pid < 0) {
				        perror("fork");
				        exit(1);
  				}

     				if (pid == 0)   //child process
				{					

					
					/* The sd2 has data available to be read */
					close(sd);
					n = recv(sd2, buf, sizeof(buf), 0);
					
					printf("received size: %d", n);
					printf("%d", buf);
					close(sd2);
				}
    				else		//parent process
				{
					printf("This is the parents");
					close(sd2);
				}
         				
   			}

		}
		else if (result < 0) {
			/* An error ocurred, just print it to stdout */
			perror("select");
		}
		else if (result == 0){

			printf("select is resulting 0");
		}		

	}

thank you for all the help

select() destroys the fds bitset and you never reinitialize it. You have to do it every time through the outermost loop.

There might be other problems -- I haven't looked carefully.

thx for the fast reply.

I think I got the thing working with one little problem. Right now the code looks like the following with your modification suggestion.

Code:

	while (1) {

   		
		result = select(sd+1, &fds, NULL, NULL, NULL);
		FD_SET(sd, &fds);

		if (result > 0) 
		{

	 		if (FD_ISSET(sd, &fds)) 
			{

				alen = sizeof(cad);
				if ( (sd2=accept(sd, (struct sockaddr *)&cad, &alen)) < 0) {
					fprintf(stderr, "accept failed\n");
					exit(1);
				}

				//make child process
				printf("forking now\n");
				pid = fork();

				if (pid < 0) {
				        perror("fork");
				        exit(1);
  				}

     				if (pid == 0)   //child process
				{					

					printf("this is the child\n");
					/* The sdhas data available to be read */
					close(sd);
					n = recv(sd2, buf, sizeof(buf), 0);
					
					printf("received size: %d\n", n);
					printf("%s\n", buf);
					close(sd2);
				}
    				else		//parent process
				{
					printf("This is the parents\n");
					close(sd2);
				}
         				
   			}
			else
			{
				printf("WTF");
				
			}

		}
		else if (result < 0) {
			/* An error ocurred, just print it to stdout */
			perror("select");
		}
		else if (result == 0){

			printf("select is resulting 0\n");
		}		





	}

I got the server receive something from the client successfully, but I can open receive the msg one time and then it keep printing me bad file descriptor. I tried removed the while loop and it works perfectly fine( print one time). Is there something wrong I need to watch out for as well?

problem solved.

it was a silly mistake...forgot to check the EINTR.

thank you for all the help

Originally Posted by saipkjai

problem solved.

it was a silly mistake...forgot to check the EINTR.

thank you for all the help

Eh? Why were you receiving a signal?